1. Field of the Invention
The present invention relates to a radial tire, more particularly to a radial tire with improved riding comfort and driving stability.
2. Description of the Prior Art
In general, the performance of a radial tire may be improved if the tread of the tire is very stiff. However, this reduces driving stability because the radial carcass cords of a tire tend to weaken the lateral stiffness of the sidewall of the tire. In such cases, the driving stability may be improved in a number of ways, for example, by changing the material and the number of the carcass cords, by changing the rubber material of the sidewall, by supplementing cord layers to strengthen the bead or by redesigning the mold profile of the tire. The driving stability may be improved by modifying the beadfiller profile.
More recently, driving stability has been improved by raising the height of the beadfiller or lowering the cross-sectional height of the beadfiller by using a light beadfiller. However, this may cause the lateral stiffness and the vertical stiffness of the tire to increase thereby adversely affecting riding comfort.
Japanese Patent Laid-Open No. 55-110604 published in 1980 and Japanese Patent Laid-Open No. 61-303392 published in 1986 seek to address these problems. Therein, the ratio of USH to SH (the ratio of upper cross-sectional height to cross-sectional height upon mounting the radial tire on the rim and filling to normal internal pressure) of the carcass profile was increased to enhance both riding comfort and steering stability.
Whilst prior art techniques may, in general, be able to improve certain characteristics of a radial tire, they may at the same time adversely affect other important features such as driving stability and cornering forces or steering stability. A further drawback is that in order to improve the specific performance level of a tire, a tire designer has to design a modified carcass form appropriate for this specific performance, and also consider both the form and hardness of the beadfiller to keep the desired shape of the carcass.